1. Field of the Invention
The present invention relates to an optical transmission system and an optical transmission method for performing optical transmission over an optical switching network, and more particularly, to an optical transmission system and an optical transmission method that can perform correction of skew that can occur in wavelength-multiplexed signals.
2. Description of the Related Art
Adaptation of optical interconnects is under review for interconnect systems of parallel computers such as supercomputers and signal switching in high-speed routers to avoid bottleneck (in terms of band and physical amount, for example) in electric wiring technology. The optical interconnect utilizes the broadband property of optical transmission technology. The optical interconnect is a generic term for optical data communication of extremely short distance. In general, the optical interconnect means optical communication of a distance shorter than a Local Area Network (LAN).
Many of optical interconnect systems introduced until now adopt switching techniques in which optical signals are once converted to electrical signals for switching. With this configuration, however, broadening of the bandwidth entails increase in the number of switching ports, and increase in the scale of switching itself. Accordingly, attempts are being made to realize optical packet switches which perform switching directly on optical signals.
On the other hand, a system for time-multiplexing optical packet/burst signals in an optical region is utilized in Passive Optical Network (PON) technology which is introduced as an optical system for subscriber system. This time-multiplexing system is introduced into a system which transmits the optical packet/burst signals in timeslots assigned to respective subscribers and terminates at the side of a communication station.
However, when signals are switched and merged in the optical region, the absence of a buffer element (delay element) which can hold the optical signals as they are causes skew to occur in the optical packets arriving at the input ports of the switch and the merging unit. As a result, a guard period allocated between transmitted packets increases. Since no information is transmitted during the guard period, the increase in guard period adversely affects optical packet transmission efficiency significantly.
To prevent the increase in guard period, Japanese Patent Application Laid-Open No. 2006-279362 proposes a technique according to which a time difference is corrected by detecting synchronization of a looped back optical dummy packet after a switching process at an optical switch node and varying the readout time until synchronization is achieved.
However, when an optical packet signal in which signals of different wavelengths are multiplexed is used in the interconnect system using the optical packet switching described above to efficiently increase the band, a skew occurs in the wavelength-multiplexed signal before it arrives at a destination node.